The position looks good for White now. If Black takes on g2, then the knight goes to f5 and later to d6. But Keymer finds a wonderful move.
5... g6h4 This is Black's idea: The pawn on g2 cannot be protected. Now White should make room for the rook on e1, but Caruana takes a drastic decision. 6. c2c4  6... d5c4  7. d1a4  7... c7c6 The pawn on g2 is still impossible to protect, but Caruana has an idea.